My advice is start with airlaw and work through. Most schools will require you to have passed airlaw prior to solo circuits. Skip navigation until you start flying it because it will make more sense plus you will need a map (which will go out of date if you buy it too soon) and a CRP-1 (flight computer), as well as some rulers etc. I think you need to find out for yourself what would suit you equipment wise, don't just buy a student pack thinking it will contain everything you need. I did just that and ended up buying a fair few things seperately that were more suited. See what your instructors use or recommend first before buying kneeboards/ flightboards and rulers, plotters etc. Don't be too eager to buy things early because you will more than likely buy something which you have no use for later on.
I've not used the Pratt books but you will find several exam subjects contained in each one. For example Navigation and Meteorology are two seperate exam subjects but are included in the same book. The divisions should be pretty clear.
Good luck with it all!